Patent GB-1156643-A (GB)
Title: Flash Welding
IPC: B23K11/24
Filed: 1967-06-05
Abstract: 1,156,643. Flash-welding. AMERICAN WELDING & MFG. CO. 5 June, 1967 [8 June, 1966], No. 25777/67. Heading B3R. In a method of flash welding, a first workpiece is located a fixed distance from a second workpiece, a voltage is applied between the workpieces which are moved relatively towards each other, at a rate which varies exponentially with time, the rate of movement is changed when the workpieces are separated by a predetermined distance, and they are pressed together with a predetermined force to therefore form a flash between the workpieces. The flash welder 12, Fig. 1, has a fixed work holding platen, and a work holding platen movable by hydraulic cylinders, which are controlled during the flashing stage by signals received from a servo amplifier 14, and after the flashing stage, by an upset control unit 16. Attached to the movable platen is a digital transducer 26 which generates pulses proportional to the linear movement of the platen, and also an analogue transducer 28 which provides a negative voltage proportional to the motion of the platen. The voltage provided by transducer 28 to amplifier 14 indicates the actual position of the movable platen and is added to the signal received from a switching ciruit 30, and gives rise to the signal which controls the platen control unit 10 during the flashing stage. Amplifier 14 responds to the difference in signals supplied through conductors 20, 22 so as to move the platen until the signals are equal. The pulses from transducer 26 are applied to a counter 32 which applies pulses over one of the four conductors 34A-34D, and these pulses along with a timer 42 control the time at which signals are applied to conductor 22 by circuit 30. In operation, the movable platen moves away from the fixed platen to an adjustable starting position, the latter being controlled by a voltage supplied to circuit 30 by an opening circuit 38, and a position circuit 40. These voltages are applied to amplifier 14 through conductor 22 at a time determined by timer 42. The motion of the platen during the flashing stage is controlled by signals applied to circuit 30 from a function generator 44. The latter has four circuits 46A-46D, each of which has an adjustable parabolic-shaped voltage waveform and they are sequentially applied to circuit 30 which applies them to conductor 22 at times determined by the pulses in conductors 34A-34D. At the end of the flashing stage a signal is applied over conductor 36 to the upset control circuit 16 which activates unit 10 to rapidly move the workpieces together at a predetermined pressure, such that a weld is formed. It can be seen that the motion of the movable platen during the flashing operation is controlled by digital signals from transducer 26 and analogue signals from transducer 28. The digital signals accurately control the total length of motion, and select the velocity pattern of motion by choosing the particular velocity characteristics from the group of functions in generator 44A. A screw 124, Fig. 2, engages with movable platen 60 so as to rotate when the platen is moved, and the end of the screw is connected to the input of the digital transducer 26. The latter comprises a disc 130, rotatable on the screw, and having perforations 132, a lamp 134 mounted on one side of the disc, and a photo-cell 136 on the other side. The output from cell 136 is applied to the pulse shaping circuit 138 which applies the pulses to counter 32.